Sensor disk having radial grooves and optical assaying method using same

ABSTRACT

An optical assaying method and system having a movable sensor is described. In one aspect, the present invention is a sensing system having a rotating sensor disk coated with indicator dyes sensitized to a variety of substances. In this configuration the sensing system further includes a detector for sensing spectral changes in light received from one or more of the indicator dyes. In another aspect, the present invention is a sensing system having a surface plasmon resonance sensor disk having grooves extending radially from a center of the disk. In yet another aspect, the present invention is a sensing system including a diffraction anomaly sensor disk having a dielectric layer that varies in thickness. The present invention allows for construction of an inexpensive sensing system that is capable of easily detecting a variety of substances either in a sample or a surrounding environment. Furthermore, the present invention provides a sensing system capable of sensing multiple substances without requiring multiple sensors.

This application is a division of pending prior application Ser. No.09/342,420 filed Jun. 29, 1999, now U.S. Pat. No. 6,277,653, which is adivision of application Ser. No. 08/974,610 filed Nov. 19, 1997, nowU.S. Pat. No. 5,994,150.

FIELD OF THE INVENTION

This invention relates generally to the field of optical sensing, andmore particularly to an optical assaying method and system having amoving sensor.

BACKGROUND OF THE INVENTION

Extremely sensitive optical sensors have been constructed by exploitingan effect known as surface plasmon resonance (SPR). These sensors arecapable of detecting the presence of a wide variety of materials inconcentrations as low as picomoles per liter. SPR sensors have beenconstructed to detect many biomolecules including keyhole limpethemocyanin, α-fetoprotein, IgE, IgG, bovine and human serum albumin,glucose, urea, avidin, lectin, DNA, RNA, HIV antibodies, humantransferrin, and chymotrypsinogen. Additionally, SPR sensors have beenbuilt which detect chemicals such as polyazulene and nitrobenzenes andvarious gases such as halothane, trichloroethane and carbontetrachloride.

An SPR sensor is constructed by sensitizing a surface of a substrate toa specific substance. Typically, the surface of the substrate is coatedwith a thin film of metal such as silver, gold or aluminum. Next, amonomolecular layer of sensitizing material, such as complementaryantigens, is covalently bonded to the surface of the thin film. In thismanner, the thin film is capable of interacting with a predeterminedchemical, biochemical or biological substance. When an SPR sensor isexposed to a sample that includes the targeted substance, the substanceattaches to the sensitizing material and changes the effective index ofrefraction at the surface of the sensor. Detection of the targetedsubstance is accomplished by observing the optical properties of thesurface of the SPR sensor.

The most common SPR sensor involves exposing the surface of the sensorto a light beam through a glass prism. At a specific angle of incidence,known as the resonance angle, a component of the light beam's wavevectorin the plane of the sensor surface matches a wavevector of a surfaceplasmon in the thin film, resulting in very efficient energy transferand excitation of the surface plasmon in the thin film. As a result, atthe resonance angle the amount of reflected light from the surface ofthe sensor changes. Typically, an anomaly, such as a sharp attenuationor amplification, is exhibited by the reflected light and the resonanceangle of an SPR sensor can be readily detected. When the targetedsubstance attaches to the surface of the sensor, a shift in theresonance angle occurs due to the change in the refractive index at thesurface of the sensor. A quantitative measure of the concentration ofthe targeted substance can be calculated according to the magnitude ofshift in the resonance angle.

SPR sensors have also been constructed using metallized diffractiongratings instead of prisms. For SPR grating sensors, resonance occurswhen a component of the incident light polarization is perpendicular tothe groove direction of the grating and the angle of incidence isappropriate for energy transfer and excitation of the thin metal film.As with prism-based sensors, a change in the amount of light reflectedis observed when the angle of incidence equals the resonance angle.Previous SPR grating sensors have incorporated square-wave or sinusoidalgroove profiles.

Another highly-sensitive sensor that has been recently developed isknown as a “diffraction anomaly” sensor. Diffraction anomaly sensorsinclude a substrate and a thin metal layer which are substantially thesame as in an SPR grating sensor. In a diffraction anomaly sensor,however, a dielectric layer is formed outwardly from the metal layer andprotects the metal layer from oxidation and general degradation.Typically, a sensitizing layer is formed outwardly from the dielectriclayer. Diffraction anomaly sensors, like SPR sensors, exhibit a changein reflectivity, referred to as a diffraction anomaly, when exposed witha light beam at a particular angle of incidence. Unlike conventional SPRsensors, diffraction anomaly sensors exhibit a change in reflectivityfor light polarized parallel to the grooves of the substrate. When alight beam has an angle of incidence equal to the diffraction anomalyangle for the sensor, the diffracted light beam propagates within thedielectric layer. In this manner, the dielectric layer acts as awaveguide and a change in reflectivity is readily detected by thecontroller. The diffraction anomaly is directly affected by thethickness of the dielectric layer. The effective index of refraction atthe surface of the diffraction anomaly sensor changes in a mannersimilar to an SPR sensor when the diffraction anomaly sensor is smearedwith a sample containing the targeted substance. Furthermore, the changein the diffraction anomaly angle is strongly dependent upon the amountof targeted substance present in the sample. In this manner, thediffraction anomaly sensor exhibits a shift in the anomaly angle that iscomparable to an SPR sensor, even though the metal grating of thediffraction anomaly sensor is coated with a dielectric layer. Therefore,a quantitative measure of the targeted substance can be calculated bymeasuring the resulting shift in the anomaly angle.

In addition to individual sensors, there is considerable commercialinterest in multiple-sensor systems that are capable of detecting avariety of targeted substances, such as certain odors, vapors, gases andother chemical species, in a surrounding environment or sample. Byutilizing several sensors, such sensing systems are capable ofsimultaneously detecting several targeted substances. Othermultiple-sensor systems utilize multiple sensors to recognize thepresence of a single targeted substance. In this configuration, theburden of recognition does not lie upon a single sensor, but rests onthe sensing system's ability to properly interpret and recognize outputpatterns of the multiple sensors. Due to the use of multiple sensors,conventional multiple-sensor sensing systems are typically extremelyexpensive. Furthermore, conventional sensing systems are inherentlycomplicated and therefore are not very portable.

For the reasons stated above, and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art foran inexpensive, disposable sensing system which can assay a variety ofsubstances in a sample. There is also a need for such a system that iscompact, easy to manufacture and readily transported.

SUMMARY OF THE INVENTION

As explained in detail below, the present invention is directed to anoptical assaying method and system having a movable sensor. In oneaspect, the invention is a system for sensing a plurality of substances.The system includes a sensor having a plurality of sensitized regions,wherein each region is sensitized to at least one of the substances. Adetector is responsive to light received from the sensitized regions ofthe sensor. A motor is coupled to the sensor for moving the sensor suchthat each sensitized region moves proximate to the detector. Acontroller is coupled to the detector for calculating a measure of atleast one substance as a function of a detected change in light receivedfrom the sensitized regions of the sensor.

According to one aspect of the invention, the sensor of the sensingsystem is a rotating sensing disk driven by the motor. For example, inone embodiment the sensing system includes a sensor disk having asubstrate coated with a plurality of indicator dyes sensitized to theplurality of substances. In this embodiment, the detector is responsiveto spectral changes in light received from one or more of the indicatordyes.

In another embodiment the sensor of the sensing system is a constantgrating sensor disk having a grooved substrate and a metal layer formedoutwardly from the substrate. Furthermore, a dielectric layer is formedoutwardly from the metal layer for suppressing reflection of incidentlight having a polarization parallel to the grooves of the substrate. Inthis embodiment, the dielectric layer continuously varies in thicknessaround the circumference of the sensor disk. The controller determinesthe measure of the substance according to a change in a position aroundthe circumference of the sensor disk at which light received from thesensor disk exhibits an anomaly. The constant grating sensor disk mayhave a plurality of concentric grooves or may have a single groovespiraling from a center of the sensor disk to an outside edge of thesensor disk.

In another embodiment, the sensor of the sensing system is a radialgrating sensor disk comprising a substrate having a plurality of groovesextending radially from a center of a surface of the substrate.Furthermore, a metal layer is formed outwardly from the surface of thesubstrate and substantially conforms to the grooved surface of thesubstrate. In this embodiment, the radially extending grooves may have afixed period around a circumference of the sensor disk. As such, a lightsource scans the light beam radially across the surface of the rotatingsensor disk and the controller determines a position along a radius ofthe sensor disk for each sensitized region at which detected lightreceived from each sensitized region exhibits an anomaly. Alternatively,the radially extending grooves may have a period that varies around thecircumference of the sensor disk and the light source exposes the sensordisk with the light beam at a fixed radius from the center of therotating sensor disk.

In yet another embodiment, the motor does not rotate the sensor butlinearly translates the sensor along a length of the sensor. In thisembodiment, the sensor includes a substrate having a grooved surfacesuch that the grooves of the surface have a period that varies along thelength of the sensor.

According to one feature of the present invention, the variousembodiments of the sensor may be a diffraction anomaly sensor that isresponsive to a change in light having a polarization parallel to thegrooves of the substrate. Additionally, the sensor of the presentinvention may be a surface plasmon resonance sensor responsive to achange in light having a polarization perpendicular to the grooves ofthe substrate.

According to another aspect, the invention is a method for assaying asubstance in a sample including the step of providing a sensor diskhaving a metal diffraction grating having at least one groove, whereinthe metal diffraction is coated with a dielectric layer having athickness varying from a minimum thickness to a maximum thickness. Thesensor disk is exposed with a light beam having a polarization componentparallel to the grooves of the grating. The sensor disk is interactedwith the sample and rotated. A measure of the substance in the sample isdetermined as a function of a shift in an anomaly position around acircumference of the sensor disk at which light received from the sensordisk exhibits an anomaly.

In yet another aspect, the invention is a method for assaying asubstance in a sample including the step of providing a sensor diskhaving a metal diffraction grating having a plurality of groovesextending radially from a center of the sensor disk to an outer edge ofthe sensor disk. The sensor disk is interacted with the sample androtated. A measure of the substance in the sample is determined as afunction of a shift in an anomaly position along a radius of the sensordisk at which light received from the sensor disk exhibits an anomaly.

These and other features and advantages of the invention will becomeapparent from the following description of the preferred embodiments ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of a sensing system for assaying aplurality of substances by detecting a change in light received from arotating sensor disk;

FIG. 2 illustrates another embodiment of a sensing system for assaying aplurality of substances by detecting a change in light reflected from arotating sensor disk;

FIG. 3 is a schematic cross-sectional view of one embodiment of asurface plasmon resonance sensor disk for use in a sensing system inaccordance with the present invention;

FIG. 4 is a schematic cross-sectional view of one embodiment of adiffraction anomaly sensor disk having a metal grating coated with adielectric layer varying from a minimum thickness to a maximumthickness;

FIG. 5A is a schematic top view of one embodiment of a radial gratingsensor disk having a plurality of grooves extending radially from acenter of the sensor disk;

FIG. 5B is a schematic top view of another embodiment of a radialgrating sensor disk having a plurality of grooves extending radiallyfrom a center of the sensor disk;

FIG. 6 is a schematic top view of one embodiment of a constant gratingsensor disk having a metal grating coated with a dielectric layervarying continuously around the circumference of the sensor disk from aminimum thickness to a maximum thickness;

FIG. 7 illustrates another embodiment of a sensing system having apolarizer coupled to a sensor disk for assaying a plurality ofsubstances by detecting a change in light reflected from the rotatingsensor disk; and

FIG. 8 illustrates one embodiment of a sensing system for assaying aplurality of substances by detecting a change in light received from amovable sensor.

DETAILED DESCRIPTION

In the following detailed description, references are made to theaccompanying drawings which illustrate specific embodiments in which theinvention may be practiced. Electrical, mechanical and structuralchanges may be made to the embodiments without departing from the spiritand scope of the present invention. The following detailed descriptionis, therefore, not to be taken in a limiting sense and the scope of thepresent invention is defined by the appended claims and theirequivalents.

FIG. 1 illustrates a sensing system 10 in accordance with the presentinvention. Sensing system 10 includes detector 25, sensor disk 50 andmotor 60 having a rotatable shaft 55. As discussed in detail below, inone embodiment sensor disk 50 contains a plurality of sensitized regions(not shown) that are sensitized to a variety of substances. In anotherembodiment, however, sensor disk 50 contains a single sensitized region.

Sensor disk 50 is coupled to shaft 55 such that engagement of motor 60causes sensor disk 50 to rotate in a circular motion in a planesubstantially orthogonal to shaft 55 such that each of the plurality ofsensitized regions is sequentially rotated into proximity of detector25. In one embodiment, a controller (not shown) is coupled to detector25 for calculating a measure of a corresponding targeted substance foreach sensing region as a function of a detected change in light 70reflected by each of the sensitized regions. In this manner, sensingsystem 10 is capable of easily detecting and measuring the presence of avariety of substances without requiring multiple sensors. In anotherembodiment, the controller determines the presence of a single targetedsubstance based on a change in reflected light 70 for a plurality of thesensitized regions. The controller may comprise any suitableprogrammable logic or embedded microprocessor configured to monitordetector 25. Furthermore, if complex analysis is required, thecontroller may employ a neural network or other means for analysis.

In order to assay a sample, sensor disk 50 is typically smeared with thesample and motor 60 is engaged to rotate sensor disk 50. The controllermonitors detector 25 to determine the presence of any targeted substancein the sample. In another configuration, however, motor 60 iscontinuously engaged and the controller monitors detector 25 todetermine whether a targeted substance is present in a surroundingenvironment. In either configuration, sensing system 10 can be easilyand inexpensively manufactured.

In one embodiment, sensor disk 25 is a substrate coated with a pluralityof indicator dyes sensitized to a variety of targeted substances. Inthis embodiment, each sensitized region of sensor disk 50 includes anindicator dye such as cresol red, phenol red, thymol blue, p-xylenolblue, m-cresol purple, bromothymol blue and bromoxlyenol blue,cholorphenyl red, bromophenol blue, bromocresol purple, phenophthalein,thymolphthalein, o-cresolphthalein, alpha-naphtholphthalein,pyrocatecholphthalein and chromoxane yanine R. In this embodiment,detector 25 is a spectrophotometer capable of measuring spectral changesin the light reflected by one or more of the indicator dyes when sensordisk 250 is either smeared with a sample containing at least one of thetargeted substances or exposed to a targeted substance in thesurrounding environment. In this embodiment, the controller of sensingsystem 10 is capable of easily detecting and measuring the presence of avariety of substances without requiring multiple sensors by detectingspectral changes in the various sensitized regions as sensor disk 50rotates. Furthermore, sensing system 10 is capable of determining thepresence of a single targeted substance based on a spectral change inreflected light 70 for a plurality of the sensitized regions.

FIG. 2 illustrates another embodiment of a sensing system 210 capable ofdetecting a plurality of targeted substances in accordance with thepresent invention. Sensing system 210 includes light source 220, sensordisk 250, polarizing beamsplitter 280, detectors 260 and 265, and motor262 having rotatable shaft 255. Light source 220, such as a laser,produces light beam 225 incident upon sensor disk 250. Sensor disk 250reflects light beam 225 as light beam 270 onto polarizing beamsplitter280. Polarizing beamsplitter 280 splits light beam 270 into components285 and 290 which are incident upon detectors 260 and 265, respectively.

In one embodiment, sensor disk 250 is a surface plasmon resonance (SPR)diffraction grating sensor having a metallized diffraction grating. Inanother embodiment, sensor disk 250 is a diffraction anomaly sensorhaving a metal grating coated with a dielectric layer. Each of theseembodiments is discussed in detail below.

FIG. 3 is a schematic cross-sectional view of one embodiment of a sensordisk 350 configured as an SPR diffraction grating sensor in accordancewith the present invention. Sensor disk 350 includes substrate 300having a surface 305 formed in a groove profile. For exemplary purposesonly surface 305 is illustrated as a substantially periodic squareprofile. Other surface profiles are contemplated including sinusoidal,trapezoidal and triangular. The period of the grooves of surface 305 mayrange from less than 0.4 micrometers to over 2.0 micrometers. Thin metallayer 310 is formed outwardly from surface 305 of substrate 300 andcomprises any suitable metal such as aluminum, gold or silver. In oneembodiment, metal layer 310 comprises silver having a thickness ofapproximately 100 nm. In another embodiment a chromium layer (not shown)is first formed on substrate 300 followed by metal layer 310 in order toimprove adhesion to the substrate.

Sensitizing layer 330 is formed outwardly from layer 310. Sensitizinglayer 330 includes receptive material that is selected to interact witha predetermined chemical, biochemical or biological substance 340contained in sample 345. For example, in one embodiment sensitizinglayer 330 comprises a layer of antigens capable of trapping acomplementary antibody. Additionally, the receptive material may beeither antibodies or enzymes. Recently, several techniques have beendeveloped for attaching antigens as a receptive material to layer 310such as spin coating with a porous silica sol-gel or a hydrogel matrix.Preferably, sensitizing layer 330 is less than 100 nm thick. In oneembodiment, glass window 335 is placed over sample 345 after sensor disk350 is smeared with sample 345. In this manner, glass window 335 retainssample 345 as sensor disk 350 is spun in a circular motion yet allowslight beam 225 (FIG. 2) to enter sensor disk 250 and diffracted light250 to escape sensor disk 250 to beamsplitter 280. Preferably, window335 is coated with an anti-reflection material in order to reduceoptical effects.

FIG. 4 is a schematic cross-sectional view of one embodiment of a sensordisk 350 configured as a diffraction anomaly sensor in accordance withthe present invention. In this embodiment, sensor disk 400 includessubstrate 405 and a thin metal layer 410 which are substantially similarto the SPR grating sensor of FIG. 3. Dielectric layer 420, however, isformed outwardly from metal layer 410 and thereby protects metal layer410 from oxidation and general degradation. In this manner, metal layer410 may comprise any suitable metal and may be selected to optimizesensitivity. In one embodiment, metal layer 410 comprises silver havinga thickness of approximately 100 nm. The diffraction anomaly exhibitedby sensor disk 400 is directly affected by thickness of dielectric layer420. Dielectric layer 420 is formed outwardly from metal layer 410 andpreferably has a minimum thickness of at least 50 nm or, morepreferably, at least 130 nm. In one embodiment, sensitizing layer 430 isformed outwardly from dielectric layer 420 as shown in FIG. 4.Sensitizing layer 430 is selected to interact with at least onepredetermined chemical, biochemical or biological substance 440contained in the sample. In another embodiment, dielectric layer 420 isselected so as to interact directly with substance 440, therebyeliminating the need for sensitizing layer 430.

Like SPR sensors, diffraction anomaly sensor disk 400 exhibits a changein reflectivity when exposed with light at a particular angle ofincidence. Unlike an SPR sensor, however, the change in reflectivity ofsensor disk 400 occurs for light polarized parallel to the grooves ofgrating 410 rather than perpendicular to the grooves. The effectiveindex of refraction of sensitizing layer 430 of sensor disk 400 changesin a manner similar to an SPR sensor when sensor disk 400 is smearedwith a sample containing a targeted substance.

FIG. 5A is a top view of one embodiment of a radial grating sensor disk500 configured for operation in a sensing system in accordance with thepresent invention. A diffraction grating is formed on a surface ofradial grating sensor disk 500 such that grooves 510 extend radiallyfrom a center of radial grating sensor disk 500. Various types ofreceptive materials are formed on the diffraction grating to form aplurality of sensitized regions (not shown). The period of grooves 510increases linearly from the center to an outside edge 520 as measured bythe linear distance between adjacent grooves. Therefore, the period ofgrooves 510 remains constant at a fixed radius around radial gratingsensor disk 500. FIG. 5B illustrates a radial grating sensor disk 550having grooves 560 that extend radially yet have a period that variesaround the circumference of sensor disk 550. In these configurations, asensor disk capable of detecting a plurality of targeted substances maybe inexpensively manufactured. Furthermore, radial grating sensor disks500 and 550 may be configured as an SPR sensor or as a diffractionanomaly sensor as illustrated in FIGS. 3 and 4, respectively.

As an SPR sensor, sensor disk 500 exhibits a change in reflectivity whenexposed with light polarized perpendicular to grooves 510. As adiffraction anomaly sensor, sensor disk 500 exhibits a change inreflectivity when exposed with light polarized parallel to grooves 510.The effective index of refraction of at the surface of sensor disk 500changes when sensor disk 500 is exposed to a targeted substance. Thechange in the index of refraction in turn changes the period of thegrating at which the reflective anomaly occurs. For a fixed wavelengthof incident light, the magnitude of the change is strongly dependentupon the amount of targeted substance present in the sample. In summary,a quantitative measure of the targeted substance can be calculated bymeasuring the resulting shift in the grating period at which surfaceplasmon resonance occurs.

Referring again to FIG. 2, as an SPR sensor disk having groovesextending radially from a center, sensor disk 250 of FIG. 2 experiencesa change in reflectivity when: (1) a component of the polarization oflight beam 225 is perpendicular to the radial groove direction, and (2)the angle of incidence and period of the grooves is appropriate forenergy transfer and excitation of surface plasmons in thin metal film ofsensor disk 250. As a diffraction anomaly sensor, sensor disk 250experiences a change in reflectivity when a component of thepolarization of light beam 225 is parallel to the radial groovedirection. For either embodiment, light beam 270 exhibits a reflectiveanomaly at a position located a radial distance from a center of sensordisk 250 whereat the period of the grooves of sensor disk 250 isappropriate for resonance. In other words, because in this embodimentsensor disk 250 has grooves extending radially from center, the radialdistance at which the change in reflectivity occurs shifts when sensordisk 250 is exposed to a targeted substance.

The new “anomaly position” for radial grating sensor disk 500 of FIG. 5Ais readily determined by translating radiation source 220 such thatlight beam 225 scans sensor disk 250 from the center of sensor disk 250toward an outside edge. Alternatively, radiation source 220 istranslated such that light beam 225 scans from the outside edge ofsensor disk 250 toward the center of sensor disk 250. The anomalyposition for radial grating sensor disk 550 of FIG. 5B varies around thecircumference of sensor disk 550, thereby eliminating the need fortranslating radiation source 220.

For either embodiment of radial grating sensor, polarizing beamsplitter280 splits light beam 270 such that component 285 has a polarizationparallel to the grooves of the surface of sensor disk 250 and component290 has a polarization perpendicular to the grooves of the surface ofsensor disk 250. A controller (not shown) monitors detectors 260 and 265and continuously calculates the ratio of the intensities of lightcomponents 285 and 290 received by detectors 260 and 265, respectively.In this manner, light fluctuations of radiation source 220, or othersystem variations such as ripples in the sample do not affect thecalculation of the targeted species in the sample. Based on thecalculated ratio of detector 260 and 265 for each sensitized region ofsensor disk 250, the controller determines a corresponding anomalyposition at which a reflective anomaly occurs. Based on the respectiveanomaly position for each sensitized region, the controller calculates ameasure of targeted substance corresponding to the sensitized region.Alternatively, the controller monitors the anomaly positions for eachsensitized region and sounds an alarm when the calculated measure of thecorresponding targeted substance exceeds a predetermined threshold.After sensing is complete, sensor disk 250 may be disposed or may bewashed and reused.

When sensor disk 250 is an SPR diffraction grating sensor the followinggeneral equation can be used for determining the anomaly position atwhich surface plasmon resonance occurs:${p\left( \frac{m\quad \lambda}{n_{0}} \right)}\left\lbrack \frac{{\cos \quad \varphi_{SP}\sin \quad \theta_{SP}} + \sqrt{\left( \frac{n_{m}^{2} - K_{m}^{2}}{n_{0}^{2} + n_{m}^{2} - K_{m}^{2}} \right) - {\sin^{2}\varphi_{SP}\sin^{2}\theta_{SP}}}}{\left( \frac{n_{m}^{2} - K_{m}^{2}}{n_{0}^{2} + n_{m}^{2} - K_{m}^{2}} \right) - {\sin^{2}\theta_{SP}}} \right\rbrack$

In this equation θ_(SP) is the polar angle and φ_(sp) is the azimuthalangle of light beam 225 with respect to the grooves of sensor disk 250,n_(o) is the index of refraction of the sample, n_(m)+iK_(m) is theindex of refraction for the metal layer, λ is the wavelength of lightbeam 225, p is the period of the grooves of sensor disk 250 and m is aninteger. When the plane of incidence of the light beam 225 isperpendicular to the radially extending grooves, i.e. φ_(sp) equals 0°,the general equation can be simplified to the following equation forcalculating the track pitch at which SPR occurs:$p = {\frac{\left( \frac{m\quad \lambda}{n_{0}} \right)}{{{- \sin}\quad \theta_{SP}} \pm \sqrt{\left( \frac{n_{m}^{2} - K_{m}^{2}}{n_{0}^{2} + n_{m}^{2} - K_{m}^{2}} \right)}}.}$

When sensor disk 250 is a diffraction anomaly grating sensor thefollowing general equation can be used for determining the anomalyposition at which the resonance occurs:$d = {\left( \frac{1}{2i\sqrt{{ɛ_{1}k_{0}^{2}} - k_{x}^{2}}} \right){\ln \quad\left\lbrack \frac{\begin{matrix}\left( {{ɛ_{1}\sqrt{{ɛ_{1}k_{0}^{2}} - k_{x}^{2}}} + {ɛ_{0}\sqrt{{ɛ_{0}k_{0}^{2}} - k_{x}^{2}}}} \right) \\\left( {{ɛ_{2}\sqrt{{ɛ_{2}k_{0}^{2}} - k_{x}^{2}}} + {ɛ_{1}\sqrt{{ɛ_{1}k_{0}^{2}} - k_{x}^{2}}}} \right)\end{matrix}}{\begin{matrix}\left( {{ɛ_{0}\sqrt{{ɛ_{0}k_{0}^{2}} - k_{x}^{2}}} - {ɛ_{1}\sqrt{{ɛ_{1}k_{0}^{2}} - k_{x}^{2}}}} \right) \\\left( {{ɛ_{2}\sqrt{{ɛ_{2}k_{0}^{2}} - k_{x}^{2}}} - {ɛ_{1}\sqrt{{ɛ_{1}k_{0}^{2}} - k_{x}^{2}}}} \right)\end{matrix}} \right\rbrack}}$

In this equation, d is the thickness of the dielectric layer, ε₀ is thedielectric constant of the medium above sensor disk 250, such as air orwater, etc., ε₁ is the dielectric constant of the dielectric layer, andε₂ is the dielectric constant of the metal layer. Furthermore, k₀ is awavevector of incident light in vacuum and equals 2π/λ. The wavevectork_(x) is determined from the equation:$k_{x} = \sqrt{\left\lbrack {{\left( {n_{0}k_{0}} \right)\sin \quad \theta_{SP}} + {\left( \frac{2\pi \quad m}{p} \right)\quad \cos \quad \varphi_{SP}}} \right\rbrack^{2} + \left( {\frac{2\pi \quad m}{p}\sin \quad \varphi_{SP}} \right)^{2}}$

In this equation, θ_(SP) is the polar angle and φ_(sp) is the azimuthalangle of light beam 225 with respect to the grooves of the surface ofsensor disk 250, where 0° azimuth corresponds to the plane of incidenceperpendicular to the groove direction, n_(o) is the index of refractionof the medium above sensor disk 250, p is the period of the grooves ofsensor disk 250 and m is an integer.

FIG. 6 is a top view of one embodiment of a constant grating sensor disk600 configured for operation in a sensing system in accordance with thepresent invention. Similar to radial grating sensor disk 500 describedabove, constant grating sensor disk 600 may be configured as an SPRsensor or as a diffraction anomaly sensor as illustrated in FIGS. 3 and4, respectively. Unlike radial grating sensor disk 500 of FIG. 4,constant grating sensor disk 600 has a diffraction grating formed withgrooves having a constant period. In one embodiment, the grooves ofsensor disk 600 are formed in a continuous spiral beginning at a centerof sensor disk 600 and spiraling outward until reaching outside edge630. In another embodiment, the grooves of sensor disk 600 comprise aplurality of concentric grooves. A dielectric layer is formed on thegrating of sensor disk 600 having a thickness that continuouslyincreases in a counterclockwise direction such that sensing region 610has a minimum thickness and sensing region 620 has a maximum thickness.As a diffraction anomaly sensor, it is preferable that the dielectriclayer has a minimum thickness of at least 50 nm or, more preferably, atleast 130 nm. As an SPR sensor, the dielectric layer must be less than50 nm thick so as to not suppress the surface plasmon resonance.

When constant grating sensor disk 600 is smeared with a sample, theanomaly position at which a change in reflectivity is exhibited shiftsaround the circumference of constant grating sensor disk 600. Therefore,the minimum thickness and maximum thickness of the dielectric around thecircumference is selected such that change in reflectivity is readilydetectable yet occurs within the circumference of constant gratingsensor disk 600. Otherwise stated, the thickness of the dielectric layerhas a gradient that insures the shift in the anomaly position is readilydetectable, but not so large as to shift outside the range of thedielectric thickness.

Referring again to FIG. 2, as a diffraction anomaly sensor having agrating with a constant groove period, sensor disk 250 exhibits a changein reflectivity when exposed with light beam 225 for light polarizedparallel to the grooves of the diffraction grating. As an SPR sensorhaving a grating with constant groove period, sensor disk 250 exhibits achange in reflectivity when exposed with light beam 225 for lightpolarized perpendicular to the grooves of the diffraction grating. Inthese embodiments, light beam 225 strikes sensor disk 250 at a fixedradius and a fixed angle of incidence. At a specific thickness of thedielectric layer of sensor disk 250 component 285 exhibits a reflectiveanomaly. Because the anomaly is a function of the thickness of thedielectric layer, the anomaly position shifts around the circumferenceof constant sensor disk 250 and not along a radius as for a radialgrating sensor. Based on the calculated ratio for each sensing elementfor detector 260 and 265, the controller determines the new anomalyposition at which a reflective anomaly occurs and calculates a measureof the targeted substance in the sample based on the new anomalyposition. In order to determine the new anomaly position along thecircumference of sensor disk 250, a detectable index mark (not shown) orother similar timing markings may be formed on sensor disk 250.Alternatively, a phase shift in a phase lock loop controlling motor 260may be directly measured to determine the new anomaly position.

FIG. 7 illustrates another embodiment of a diffraction anomaly sensordisk 750 having a linear grating wherein the grooves 752 aresubstantially parallel. This embodiment may be advantageous in that sucha sensor disk may be simpler and less expensive to manufacture than asensor disk having either concentric grooves or a spiral pattern. Inthis configuration, however, the plane of the incident light iscontinually changing as sensor disk 750 is rotated, thereby foreclosingthe use of a stationary polarizing beamsplitter. FIG. 7 illustrates oneembodiment of a sensing system 710 capable of detecting a plurality oftargeted substances using a sensor disk 750 having a linear diffractiongrating. Sensing system 710 includes light source 720, sensor disk 750,motor 760, shaft 755, polarizer 770 and detector 765. In thisconfiguration, polarizer 770 is coupled to sensor disk 750 such thatboth polarizer 770 and sensor disk 750 are both rotated by motor 760 andshaft 755. Sensor disk 750 includes a grating having a grooved surfaceand may be configured as an SPR sensor or a diffraction anomaly sensoras described in detail above. Furthermore, polarizer 770 is orientedwith respect to sensor disk 750 such that the polarization of theincident light is perpendicular to the grooves of the grating of sensordisk 750 for SPR sensing, or parallel to the grooves of the grating ofsensor disk 750 for diffraction anomaly sensing. Preferably, light beam725 is initially unpolarized or circularly polarized so that there islittle variation in transmission through polarizer 750 as it rotates.

FIG. 8 illustrates a sensing system 810 in accordance with the presentinvention. Sensing system 810 includes light source 820, sensor 850,polarizing beamsplitter 880, detector 860 and detector 865. Light source820, such as a laser, produces light beam 825 incident upon sensor 850at an incident position. Sensor 850 reflects light beam 825 as lightbeam 870 onto polarizing beamsplitter 880. Polarizing beamsplitter 880splits light beam 870 into component 885 and component 890 which areincident upon detector 860 and detector 865, respectively. In oneembodiment, sensor 850 is a surface plasmon resonance (SPR) sensorhaving a metallized diffraction grating. In another embodiment, sensor850 is a diffraction anomaly sensor having a metal grating coated with adielectric layer. For either embodiment, radiation source 820,polarizing beamsplitter 880, detector 860 and detector 880 operatesubstantially as described for sensing system 210 of FIG. 2.

Sensor 850 may have a plurality of regions (not shown) sensitized to atleast one targeted substance. Furthermore, sensor 850 contains aplurality of substantially parallel grooves 855 having a period thatvaries along a length of sensor 850. After sensor 850 is exposed to asample, sensing system 810 translates sensor 850 such that the period ofgrooves 855 at the incident position of light beam 825 changes. Theanomaly position at which a change in reflectivity occurs shifts alongthe translation direction according to the amount of targeted substancepresent in the sample. The controller calculates a measure of thetargeted substance for each sensitized region of sensor 850 based on theshift in anomaly position for each sensitized region of sensor 850.

Several embodiments of an optical assaying method and system having arotating sensor disk have been described. In one aspect, the presentinvention is a sensing system having a sensor disk coated with indicatordyes sensitized to a variety of substances. In this configuration thesensing system includes a spectrophotometer for detecting spectralchanges in light reflected by one or more of the indicator dyes. Inanother aspect, the present invention is a sensing system having asurface plasmon resonance sensor disk having grooves extending radiallyfrom a center of the disk. In this embodiment, various types ofreceptive material are formed on the diffraction grating of the sensordisk to form a plurality of sensitized regions. In yet another aspect,the present invention is a sensing system including a diffractionanomaly sensor disk having a dielectric layer that varies from a minimumthickness to a maximum thickness.

The several advantages of the present invention include facilitatingconstruction of an inexpensive sensing system capable of easilydetecting a variety of substances either in a sample or a surroundingenvironment. Furthermore, the present invention provides a sensingsystem capable of sensing multiple substances without requiring the useof multiple sensors. This application is intended to cover anyadaptations or variations of the present invention. It is manifestlyintended that this invention be limited only by the claims andequivalents thereof.

We claim:
 1. A radial grating sensor disk, comprising: a substratehaving a plurality of grooves in a surface, wherein the grooves extendradially from a center of the surface; a metal layer formed outwardlyfrom the surface of the substrate, the metal layer substantiallyconforming to the grooved surface of the substrate; and a sensitizinglayer formed outwardly from the metal layer wherein the sensitizinglayer is selected for interacting with at least one substance in asample.
 2. The disk of claim 1, wherein the grooves of the substratehave a constant period around a circumference of the sensor disk.
 3. Thedisk of claim 1, wherein a period of the grooves of the substrate variesaround a circumference of the sensor disk.
 4. A method for assaying asubstance in a sample comprising the steps of: providing a sensor diskhaving a metal diffraction grating having a plurality of groovesextending radially from a center of the sensor disk to an outer edge ofthe sensor disk; interacting the sensor with the sample; rotating thesensor disk; and determining a measure of the substance in the sample asa function of a shift in a position along a radius of the sensor disk atwhich light received from the sensor disk exhibits an anomaly.
 5. Themethod of claim 4, wherein the grooves of the substrate have a constantperiod around a circumference of the sensor disk.
 6. The method of claim4, wherein the grooves of the substrate have a period which variesaround a circumference of the sensor disk.